​​A manifold of degradation mechanisms causes premature capacity fade of Li-ion batteries. To understand their origin, we need a detailed diagnosis of battery (mal-)function over time. Here we employ correlative neutron and X-ray imaging to observe microstructural changes over time inside high energy density cylindrical cells and focus on unraveling the causes of localized defects where the silicon-graphite anode becomes damaged.

In the study, a team of researchers led by the CEA-IRIG, the ILL and the ESRF in collaboration examined Li-ion batteries during their lifetime using state-of-the-art, non-intrusive imaging techniques available at neutron and X-ray sources, respectively the Institut Laue Langevin (ILL). Their sophisticated combination allowed to gain multidimensional information on the components and elements inside working battery cells.

The team identified macroscopic deformations in the wound structure of the copper current collector. The deformed areas already existed in fresh battery cells that only went through the initial activation cycle (the first charging-discharging cycle). Further investigations revealed that these defects are due to local accumulations of silicon occurring during electrode manufacturing. Upon activation, the largest agglomerates expand heavily, which leads to deformations in the current collector, wasting capacity before the cell ever went into use.

This kind of approach is at the heart of the Battery Hub created in Grenoble by the CEA, the ESRF and the ILL as a European platform for battery diagnosis and investigations using standardised, integrated and multi-technique workflows.